Characterization of the Agro-Climatic Environments of Drylands
- Defining the Dryland Agro-Climatic Environment
Drylands are not defined merely by low rainfall, but by:
- High variability and uncertainty in precipitation.
- High atmospheric demand for water (evapotranspiration).
- Permanent moisture deficit, which dictates specific farming systems.
Core Defining Parameter: Moisture Availability
- Aridity Index (AI): Ratio of Annual Precipitation (P) to Potential Evapotranspiration (PET).
- Dryland Agriculture occurs in regions with AI = 0.20 – 0.50.
- This implies that only 20–50% of the water lost to the atmosphere is replenished by rainfall.
- Key Characteristics of Dryland Agro-Climates
(i) Low and Erratic Rainfall
- Fact: Drylands receive <750 mm annual rainfall (arid zones <500 mm).
- Implication: Insufficient for most crops without soil moisture conservation.
- Critical Point: Rainfall reliability is a greater challenge than total rainfall. Example: A region may average 600 mm, but receive 300 mm one year and 900 mm the next.
(ii) High Temporal and Spatial Variability
- Temporal (Within a Season): 70–80% of rainfall may occur in just 20–30 rainy days during monsoon. Implication: Narrow sowing window; delays of even one week can cause crop failure.
- Spatial (Across a Region): Rainfall is highly localized (e.g., scattered thunderstorms). Implication: Makes large-scale drought management difficult.
(iii) High Temperature and Evapotranspiration (ET)
- Fact: Drylands face high temperature, intense solar radiation, and low humidity.
- Implication: PET often >1500–2000 mm/year, much higher than rainfall.
- Example: Rainfall = 600 mm; PET = 1800 mm → severe moisture deficit.
(iv) Frequent Drought Occurrences
- Fact: Meteorological droughts are common. In India, drought occurs every 2–5 years; in Rajasthan, almost every alternate year.
- Implication: Drought is a recurring feature, not an exception → risk mitigation is essential.
(v) Soil Characteristics
- Low Organic Matter: <0.5% due to sparse vegetation and high decomposition.
- Erosion-Prone: Intense rains + poor ground cover → wind & water erosion.
- Shallow Depth: Many regions (e.g., Deccan Plateau) have shallow soils with hardpan/rock → limits root growth & water storage.
- Agro-Climatic Zoning of Drylands in India
Agro-Climatic Zone |
Key Features |
States |
Farming Systems & Crops |
Western Dry Region |
Arid (<300 mm), High ET |
W. Rajasthan, N. Gujarat |
Dry farming, fallowing, water harvesting. Crops: Pearl millet (Bajra), Cluster bean (Guar), Moth bean. |
Deccan Plateau |
Semi-Arid (500–750 mm), Shallow soils |
Maharashtra, Telangana, N. Karnataka |
Contour bunding, intercropping. Crops: Sorghum (Jowar), Sunflower, Chickpea (Chana). |
Central Plateau |
Semi-Arid (700–1000 mm), Problematic soils |
MP, E. Rajasthan, UP |
Watershed management. Crops: Soybean, Pigeon pea (Arhar), Wheat (residual moisture). |
Rain Shadow Region of Eastern Ghats |
Semi-Arid (600–850 mm) |
Tamil Nadu, Andhra Pradesh |
Dryland farming. Crops: Groundnut, Pulses, Millets. |
- Summary: Core Features of Dryland Agro-Climate
Feature |
Description |
Impact on Agriculture |
Precipitation |
Low (<750 mm), Erratic, Unpredictable |
High risk of crop failure; dictates sowing time |
Aridity Index |
0.2 – 0.5 |
Permanent soil moisture deficit |
Evapotranspiration |
Very High (>1500 mm/year) |
Rapid loss of stored soil moisture |
Drought Probability |
High (every 2–5 years) |
Farming must include risk mitigation |
Soil Quality |
Low organic matter, shallow, erosion-prone |
Requires soil conservation & fertility management |